class Father {
    constructor(x, y) {
        this.x = x;
        this.y = y;
    }
    sum() {
        console.log(this.x + this.y);
    }
}
class Son extends Father {
    constructor(x, y) {
        super(x, y); //调用了父类中的构造函数 
    }
}
var son = new Son(1, 2)
var son1 = new Son(11, 22)
son.sum();
son1.sum();